GC Studio M ftw
There would be blocks (graphic was attackblock.png or .gif) over the black squares. Game Coordinators (i.e. you had a whole staff team dedicated to hosting events), could specify the HP of the blocks that you would have to eliminate, or they could be specified as invincible. It was intended as a multi-purpose event room, although it probably would have done better if it was a gmap with more space for combat in a similar layout. Different events held here included CTF, maze races, team PK battles, etc (the Game Coordinators had additional tools).